Bridge arrangement



May 21,. 1935. w. BuscHBEK 2,002,338

' BRVIDGE ARRANGEMENT Filed Oct. 51, 1933 OUTPUT l NV E NTO R WfR/Vfl? 505095156X M/WL/ ATTORNEY Patented May 21, 1,935

BRIDGE ARRANGEMENT Werner Buschbeck, Berlin; Germany, assignor to V Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application October 31, 1933, Serial No. 696,067

.. In Germany August 20, 1932 .4 Claims. (01. 179-171) Itis known that, in bridge arrangements intended for short wave communication, if it is desired to obtain effective neutralization independent of the wave length, it is necessary to balance not only theinternaltube capacity between the grid andanode of the tube, but also all the lead inductances. To obtain a still greater neutralization, the grid filament capacity, as well V as the cathode lead inductance, should also be balanced. It has been found, however, that even such features, in circuit arrangements, do not provide the desired degree of neutralization where comparatively largetubes are used func-' tioning on short waves otthe order of ten meters and less. The reason for this is that the plate filament capacity. of the; tube, which is connected to ground through an inductance, "can no longer be thought of as being in parallel relation to the intermediate circuit capacity, due to the finite length of the cathode leads.

In other words, inthe case of. short waves, the tube, as such, can no longerbe considered as a combination of capacities in'delta relation. The definite length of the lead-in ior theelectrode,

or the definite length of the electrodes them-,

selves, each form capacities, gradually approaching the order of one quarter of a wave length and involving the necessity of reproducing, besides the capacities, internal self-inductive reactances, in order to attain the desired balance of the bridge independent of the frequency.

According to the present invention, the capaci-' tance in the neutralizing branch, which corresponds to the plate cathode capacitance, is also provided with a self-inductance corresponding to the self-inductance of the cathode lead circuit.- In the case of a plate neutrodyne circuit arrangement, involving a very simple tube arrangement comprising a directlyaccessible external plate, there results a scheme of the kind shown in Fig. l, or, in case of a push-pull circuit, the scheme illustrated in Fig. 2.

Fig. 1 schematically illustrates a single tube circuit, equipped in accordance with the present invention, and its equivalent bridging circuit;

' Fig. 2 schematically illustrates the invention as applied to a push-pull circuit arrangement and its equivalent bridge circuitj and Fig". 3 illustrates a similar bridge arrangement for a plurality of tubes, except that counter cou the static value because of their finite length-Z which gradually assumes values comparable-with the wave length. Inasmuch as the tube capacitanccs, generally speaking, are formed'by cylindrical condensers, their dynamic reactance value is easily indicated quantitatively by where D and d the diameters of the cylinders constituting the capacity, Zn stands for natural logarithm, A equals the wavelength, and Z is the length of the cylinder. This reactance value, for longer wave involving, as will be understood, very small angles (for which ctgc; becomes simply l/a) changcsinto the value determinable from the static capacity,"

a 9.60% D 'l a-e The equation shows that, iiindependence of the wave length is to be assured for thebridge balance also inside the rangeof ultra short waves,

the distribution of L and C in the compensating capacities must be chosen similarly as in the tube, in other words, that the surge impedances (characteristic impedances) of the compensation capacities must as closely as feasible be equal to those of the tube capacitances to be equalized or compensated.

Neutralization independent of and unaffected by thewave length is of advantage not only when working within the ranges of ultra short waves,

indeed, itaffords also inside the medium and long press short parasitic phenomena in the case of push-pull schemes.

Fig. 1 shows the arrangement in the ordinary manner of representation. However, for the sake of simplicity, the capacities and selfeinductances forming the equivalent bridge arrangement are also shown in Fig. 1 schematically. In this figure the capacity NAG corresponds with the ordinary anode-grid neutralizing capacity, NGK corresponding with the grid-cathode capacity CGK etc. In an analogous manner, the balancing selfinductances SG, SK correspond with the self-inductances Lo and LK of the tube.

I A further improvement of the arrangement re- 0 sides in the fact that the neutralizing capacities NAG, NAK, and NGK are not formed of practically pure capacities, but include the same distributed self-induction as found in the internal tube capacities to be neutralized, and accordingly the neutralizing capacities will have a wave resistance equal to that of the capacities to be neutralized.

The difierences due to dynamic and static capacity already apparent at a wave length of 5 m by using a lil-kW-water cooled tube, will be elucidated by the following example: Assuming that the inner diameter D of the cylindrical anode is 7 cm and the grid diameter" at 2,5 cm, the length of the grid mounting 35 cm, then according to the formula outlined above, the blind resistance calculated from the static capacity will be 141 ohms, and the dynamic blind resistance actually present at the grid input within the tube will be 133 ohms. This indicates that even in considering the self-induction of the input lead within the tube, the bridge is detuned by an amount of 6% against the longer waves due to the distributed self-inductions of the grid mounting alone at 5 in wavelength, a value which in case of steep tubes (particularly in transmitter stages with several tubes), may quite readily lead to self excitation and disturbing waves.

Figs. 2a and 21) exhibit the same inventive idea for the ordinary, as well as for the bridge arrangement for a push-pull stage.

It will be understood that such a bridge arrangement compensated as described in reference to all three internal tube capacitances may be provided with counter-coupling capacities which will not disturb the balance of the bridge, as

shown in Figure 3.

I claim:

1. A neutralizing circuit of bridge form for an electron discharge device having an anode, cathode, and grid, and a condenser in the output circuit of said devices connected between said anode and cathode, comprising a first inductance of a value substantially equal to the self-inductance of the lead in the device connected to the grid, a second inductance of a value equal to the self-inductance of the lead in the device which is connected to the cathode, a direct connection from one terminal of said first inductance to said grid lead, and a direct connection from one terminal of said second inductance to said cathode,

the other terminals of said two inductances being connected together through a condenser whose value is equal to the value of the internal capacity between said grid and cathode electrodes, and two serially connected condensers arranged in parallel with respect to said first condenser, one of said two serially arranged condensers having a value substantially equal to the value of the internal capacity between said anode and grid,

and the other of said twocondensers having a value substantially equal to the internal capacity between said anode and cathode, and a connection between the junction point of said two condensers and said output circuit. v

2. A neutralizing circuit in accordance with claim 1, characterized in thisthat said condenser, whose value is equal to thefinternal capacity between said anode and grid, has one of its plates directly connected to said first inductance, and said condenser, whose value is substantially equal to the value of the internal capacity between the connected to said second inductance; said cir-.

cuit including a capacitive connection between the junction point of said two condensers and said one terminal of said second inductance.

. 3. A neutralizing circuit of bridge form for an electron discharge device having an anode, cathode, and grid, and a condenser in the output circuit of said devices connected between said anode and cathode, comprising a first inductance of a value substantially equal to the self-inductance of the lead in the device connected to the grid,

a second inductance of a value equal to the selfinductance of the lead in the device which is connected to the cathode, a direct connection from one terminal of said first inductance to said grid lead, and a direct connection from one terminal of said second inductance to said cathode, the other terminals of said two inductances being connected together through a condenser whose value is equal to the value of the internal capacity betweensaid grid and cathode electrodes, and two serially connected condensers arranged in parallel with respect to said first condenser, one of said two serially arranged condensers having a value substantially equal to the value of the internal capacity between said anode and'grid, and the other or" said two condensers having a valuesubstantia-lly equal to the internal capacity. between said anode and cathode, and a connection between the junction point of said two condensers and said output circuit, and a network including elements of substantially identical characteristics with arrangements similar to those of said electron discharge device and its associated elements symmetrically connected to said device to form, in efifect, a push-pull system.

4. A neutralizing circuit of bridge form for an electron discharge device having an anode, cathode, and grid, and a condenser in the output circuit of said devices connected between said anode and cathode, comprising a first inductance of a value substantially equal to the self-inductance of the lead in the device'connected to the grid, a second inductance of a value equal to the selfinductance of the lead in the device which is connected to the cathode, a direct connection from one terminal of said first inductance to said grid lead, and a direct connection from one terminal of said second inductance to said cathode, the other terminals of said two inductances being connected together through a condenser whose value is equal to the value of the internal capacity between said grid and cathode electrodes, and two serially connectedv condensers arranged in parallel with respect to said first condenser, one of said two serially arranged condensers having a value substantially equal to the value of the internal capacity between said anode and grid, and the other of said two condensers having a value substantially equal to the internal capacity between said anode and cathode, and a connection between the junction point of said two condensers and said output circuit, and another electron discharge device having similar elements similarly arranged and of similar values to those of said first device, both of said devices being symmetrically connected together inpushpull fashion.

WERNER BUSCI-IBECK. 

